The potent family of antibacterial and antitumor agents known collectively as the calicheamicins or the LL-E33288 complex, are disclosed in U.S. Pat. No. 4,970,198 (1990). The compounds contain a methyltrisulfide that can be reacted with appropriate thiols to form disulfides while at the same time introducing a functional group such as a hydrazide or similar nucleophile. Examples of this reaction with the calicheamicins are given in U.S. Pat. No. 5,053,394. U.S. Pat. No. 5,770,701 is directed to a process for preparing targeted forms of disulfide compounds of the LL-E33288 complex. A linker, 4-(4-acetyl-phenoxy)butanoic acid, is condensed with calicheamicin N-acetyl gamma dimethyl hydrazide to afford the carboxylic acid-hydrazone which is further treated with N-hydroxysuccinimide to give the OSu ester (N-succinimidyloxy) which is ready for conjugation with a chosen biomacromolecule.
Previously disclosed synthetic methods for constructing calicheamicin derivatives are complicated by multiple calicheamicin containing synthetic steps having low overall yields. The calicheamicin moiety is inherently toxic, and when already part of a synthetic target necessitates increased safety precautions which must be observed during manipulation and purification of the products of each of the synthetic steps. The claimed process provides a method of fewer steps involving the calicheamicin moiety with increased yields.